You can tell a lot about how successful a Microsoft product is by the specificity or vagueness of Microsoft's public statements. While Microsoft occasionally admits failure, eventually, as it did with Windows Vista and the Kin phone, when a new product is unsuccessful Microsoft tries to send out a positive vibe even if the numbers don't back it up.

It's certainly too early to declare Windows Phone 7 a failure, but Microsoft seems reluctant to call it a success.

When I asked Microsoft how many Windows Phone 7 devices have been sold, I received this statement: "Microsoft is pleased with the response so far to Windows Phone 7 and looks forward to working with our partners to continue to promote the great experience that WP7 brings to consumers throughout the holiday season and beyond."

If Microsoft had sold 5 million Windows Phone 7 devices, or even 1 million, you can bet Microsoft would reveal those numbers without being prompted. Instead, the company isn't releasing any sales figures, which is certainly a marked difference from Apple's Steve Jobs' public statements about iPhone and iPad sales.

AT&T gave me a statement that was almost identical to the one Microsoft provided. "While we don't disclose specific sales figures, we're encouraged by the demand from customers in stores and online," AT&T said. T-Mobile offered a little more specificity, saying that while an Android phone was its biggest seller on Black Friday, "our new Windows Phone 7 offering, HTC HD7, is also among our customers' top smartphone choices."

Still, it's not impossible to get a sense of how many Windows Phone 7 devices have been sold.

TheStreet reported Microsoft sold "a mere 40,000 phones" the day of the WP7 launch, citing an anonymous market research source. A PC World report from the first day of sales said the HTC HD7 was sold out.

At least 117,000 have been sold, based on Facebook mobile application usage. DigiTimes reports Windows phone sales were "better than expected" in Europe and Australia, and that 2011 sales should take a 5.1% market share (a percentage that some speculative reports say would account for 17 million devices), much less than Microsoft's target of 30 million. (Although, Microsoft backed off its 30 million unit sales projection months ago).

Microsoft accounted for 14% of U.S. smartphone owners in October, before the launch of Windows Phone 7, according to Nielsen. iPhones, Google's Android and BlackBerries are dominating new sales, perhaps not leaving Microsoft much room for growth, but a report in Wired takes an optimistic view, saying Windows Phone 7 is "just getting started." Even the 40,000 first day sales number isn't as bad as is seems when you "consider that Windows Phone is entering a market where everyone and their mother already seems to be cradling an iPhone or an Android phone," Wired notes.

The iPhone and first popular Android phones certainly posted better initial sales, although they weren't entering a market as cluttered as the one that exists today, the Wired report continues.

It presumably won't be long until market research firms come out with some more definitive numbers showing how Windows Phone 7 is faring against iPhones, Androids and BlackBerries. For now, it may be impossible to say exactly how many Windows phones are being sold, especially since Microsoft won't say itself. If the Redmond marketing machine were happy with sales, it's hard to imagine the numbers would be such a big secret.